1. Field of the Invention
This invention relates to the separation of bitumen from tar sands and, more particularly, to a process for separating bitumen from tar sands having a relatively high viscosity.
2. The Prior Art
The term "tar sand" refers to a mixture of bitumen (tar) and sand. Alternate names for tar sands are "oil sands" and "bituminous sands", the latter term being more technically correct in that the sense of the term provides an adequate description. However, for convenience herein, the term "tar sand" will be used throughout. The bitumen of tar sand consists of a mixture of a variety of hydrocarbons and heterocyclic compounds and, if properly separated from the sand, may be upgraded to a synthetic crude oil suitable for use as a feedstock for the production of liquid motor fuels, heating oil, and/or petrochemicals.
Tar sand deposits occur throughout the world, often in the same geographical area as conventional petroleum deposits. About 65 percent of all of the known oil in the world is contained in tar sand deposits or in heavy oil deposits. Significantly large tar sand deposits have been identified and mapped in Canada, Venezuela, and the United States. The Canadian tar sands are one of the largest deposits in the world having an estimated recoverable potential of approximately 900 billion barrels and are currently being developed. About 90 to 95 percent of the mapped tar sand deposits of the United States are located within the state of Utah. The Utah tar sand deposits are estimated to include at least 25 billion barrels of oil. Although the Utah tar sand reserves appear small in comparison with the enormous potential of the Canadian tar sands, Utah tar sand reserves represent a significant energy resource when compared to the U.S. crude oil proven reserves (approximately 31.3 billion barrels) and with the United States crude oil production of almost 3.0 billion barrels during 1976.
Tar sands in Utah occur in 51 deposits generally along the eastern side of the state, although only six of these deposits are currently worthy of any practical consideration. Table I sets forth the estimated in-place bitumen in billions of barrels for each of these six major deposits. The bitumen content varies from deposit to deposit as well as within a given deposit and current information available indicates that Utah tar sand deposits averate generally less than about 10 percent bitumen (by weight) although deposits have been found with a bitumen saturation up to about 17 percent bitumen (by weight).
TABLE I ______________________________________ Extent of Utah Tar Sand Deposits In-Place Bitumen Deposit Location (billion barrels) ______________________________________ Tar Sand Triangle SE, Utah 12.5-16.0 P. R. Spring NE, Utah 4.0-4.5 Sunnyside NE, Utah 3.5-4.0 Circle Cliffs SE, Utah 1.3 Hill Creek NE, Utah 1.2 Asphalt Ridge NE, Utah 1.0 ______________________________________
Various processing strategies have been explored over the past approximately 50 years. However, because of the significant differences in the physical and chemical nature of Utah tar sands as compared to Canadian tar sands, and because of the great differences in climatic conditions between the two locations, the technology developed for the Canadian tar sands cannot be applied to Utah tar sands directly. One process that has been developed specifically for Utah tar sands is set forth in U.S. Pat. No. 4,120,776. This technology is classified under the general heading of a hot water process wherein a hot, aqueous solution having a controlled pH range is used to displace the bitumen from the sand.
An important feature of the Utah tar sands is its substantially greater bitumen viscosity in comparison to the bitumen viscosity of Canadian tar sands. For example, the viscosity of bitumen from the Asphalt Ridge deposit is about one order of magnitude greater than the viscosity of Canadian bitumen while, correspondingly, tar sand samples from the Sunnyside deposit have a bitumen viscosity that is about two orders of magnitude greater than the viscosity of the Canadian bitumen. Further, the viscosity of bitumen from a Tar Sand Triangle sample is well over four orders of magnitude greater than the viscosity of bitumen from the Canadian deposits.
While relatively good separation of the bitumen from the tar sand has been obtained using variations in the hot water separation processes, any hot water processing strategy requires substantial energy input. For example and with particular reference to FIG. 6, it is calculated that the required energy input for digestion in the hot water process (operating at 95.degree. C. and obtaining about 90 percent bitumen recovery) requires at least 45 kilowatt hours of energy per ton of tar sand processed. In the ambient temperature process of the present invention, the energy input for size reduction is substantially lower, requiring less than 13 kilowatt hours per ton of tar sand processed to achieve the same level of recovery.
In view of the foregoing, it would be a significant advancement in the art to provide an ambient temperature, physical separation process for the recovery of bitumen from Utah tar sands without reverting to a hot water process. It would also be an advancement in the art to provide a novel process for the recovery of high viscosity bitumen from Utah tar sand deposits by a simple mechanical process for phase disengagement followed by flotation for phase separation and bitumen concentration. Such a novel process is disclosed and claimed herein.